FR2692065A1 - Process for the production of industrial parts by the action of light on a liquid polymerizable or crosslinkable material without the need for supports. - Google Patents

Abstract

Method for producing a model of an industrial part by phototransformation of a curable or cross-linkable liquid organic material, comprising the addition of cured grains of material to the series of models to be fabricated, thereby eliminating completely the stage of fabricating of supports.

Description

 The present invention relates to a process for the production of industrial objects or models of parts, by the action of light and in particular by photo-transformation of a plastic or composite material.

I1 is desirable to be able to have an industrial part, such as a mechanical part, before launching mass production. Currently, to make models of such parts, it is necessary to first carry out dimensioned plans at the design office from quantified data which define the shape of the part. For several years, the method of "Conception
Computer Aided "(CAD) is used to define the shape of this part.

 It is known to provide a method and a device for producing models of industrial parts by using the encrypted data available in the output memories of the computer, directly to produce the models of parts without having to go through the 'intermediate plans or, having to involve machining machines with digital controls such as milling machines, lathes, etc ...

 Methods and devices proposed for the realization of models using CAD are based on a chemical polymerization induced by LASER. The controlled movement of one or more laser beams possibly concentrated at the same point, allows the local polymerization of an advantageously polyfunctional monomer and, step by step, the production of the part.

 For example, document [1] describes a process whose general principle of producing a part is based on the use of an apparatus comprising a tank which contains the liquid photopolymerizable monomer (or the oligomer or the mixture of the two) at the level from which a mobile platform is exposed which descends step by step during the operation. The laser beam traces successive sections of the object to be produced on the surface of the liquid, thanks to a set of electronically deflected mirrors, controlled by the CAD system database. The software previously subdivided the virtual model of the object into a multitude of thin slices. As each slice solidifies, the "sculpted" model dives slowly into the tank; with a 10 mW laser, this system makes it possible to create a part 30 mm high in 50 minutes, with an accuracy of the order of 1 / 10th of a millimeter. The model can be created in all kinds of materials, (plastics), in a wide variety of colors, with different hardnesses and a whole range of abrasion resistance [3,4].

 This type of process, which requires a material in the initial state in liquid or pasty form, has a disadvantage when it is desired to manufacture parts comprising suspended parts. Once the orientation of the part is fixed relative to the vertical (defined by gravity during the manufacturing phase), it may happen that certain portions are supported neither by another part of the part, nor by the plate on which the part rests (see figure 1).

 In this case, when the light radiation has just solidified the first part of this portion, the volume just solidified is not attached to any other solid, and is isolated in the liquid. In general, the densities of the liquid and the solid are different, and the volume risks "sinking" if the surface tension is not enough to keep it on the surface. In addition, during the establishment of the next layer of liquid, the part under construction is moved relative to the level of the liquid. This movement being made by means of the mechanical arm which supports it, it is impossible to communicate the movement to the isolated volume, which will therefore no longer be integral with the rest of the part during the rest of the manufacture.

 To solve this problem, current users of this type of process add to the part, prior to its manufacture, "supports" making it possible to make the suspended portions integral with the part or the plate which supports it (cf. FIG. 2).

Concretely, this addition is made by the modification of the database resulting from the CAD system having been used for the recommendation of the part. It should be noted that this phase is not a simple job, and has many drawbacks, for the following reasons5
- mastery of the CAD system used for the
room design is required on the part of
the user of an object making machine in?
3 dimensions, problem compounded by the fact that
there are many different CAD systems and
incompletely compatible
- the removal of supports once manufacturing
completed is a work which, if not carried out
carefully, or if the supports are placed incorrectly,
can deteriorate the part
- it is quite difficult to automate this phase, because
the placement of the supports so as to facilitate their
deletion (while ensuring the proper manufacture of
all suspended portions) requires a long
experience, difficult to formalize
- finally, some parts may have portions
very difficult to reach, making
almost impossible their manufacture by this type of
process (see Figure 3)
Other rapid prototyping methods, such as that described in document [2], solve this problem by using a solid material, which ensures that no isolated portion can "sink" or move during manufacture.

These methods however have other disadvantages compared to methods using liquid, in particular with regard to the loss of useful material during manufacture.

 The object of the present invention is to modify the liquid-based method so that it has the same advantages as the methods based on solid material, without having the disadvantages.

 The basic idea is that during manufacture, the part is no longer in a liquid medium, but on the contrary in a medium which prevents the isolated elements from flowing, makes them integral with the rest of the part, while not laying no more problem during the final extraction of the part than if the part was still in liquid.

 For that, it is a question of manufacturing an artificial medium having these properties and being at the interface between the liquid and the part.

 A first solution would be to make a gel strong enough around the part so that the isolated portions do not move, but that we can still extract the part at the end of its manufacture.

 It is a very difficult solution to put into practice, because it would be necessary to make adjustments allowing to obtain a homogeneous gel on fairly large volumes (at least to twist mm3) which is impracticable when the irradiation takes place exclusively by a only side of the volume, as is the case in the process we are talking about.

 This is why the present invention rather recommends a medium which could be described as a "wet powder", that is to say a large number of small solid elements bound by a liquid, which can be largely a minority in volume compared to the material. in solid form.

 It is quite possible to make this medium from liquid: the wet powder can after all be considered a part like any other. The manufacture of the part can therefore be done simultaneously with the manufacture of the wet powder which surrounds it, this mistletoe completely avoids the use of a support avelconque without bringing the extraction of the part at the end of the manufacture (clean this kind powder is much simpler than breaking the supports).

Let's summarize the advantages of using wet powder:
- adding wet powder to a room is extremely
simple to automate: the part only needs to be
fully enclosed (over a sufficient thickness);
- it is completely unnecessary to add supports, this
which results in a dramatic decrease in the
"IT cost of manufacturing a part
(some users of the process consider that the
manufacturing time for a somewhat complex part is
80% made up of IT work);
- the final cleaning is less likely to deteriorate the part
only when it is necessary to detach the supports therefrom;
- certain parts impossible to manufacture by this
process (for example when it is impossible
to add supports - because they could not be
removed from the part at the end of its manufacture)
become feasible, always without imposing a cost
computer science;
On the other hand, the fact of making powder at the same time as the part amounts to solidifying more volume than strictly necessary. In addition, some implementation issues need to be resolved
- the portions located on the periphery of the powdery environment
can be seen as isolated from the rest of the
piece, and they may not be attached to it
during a movement;
- the liquid must not remain polluted by
grains of powder once the part has been manufactured
finished.

 One possible solution to solve these problems consists in simultaneously manufacturing the part, a sealed enclosure around the part, and wet powder situated between the enclosure and the part (cf. FIG. 4). The purpose of the enclosure is to confine the powder, and to keep it in place when the layers are put in place.

 However, if the presence of an enclosure makes it possible to prevent migration of the powder towards the tank, it does not ensure that inside the enclosure the powder is perfectly immobilized. However, even a slight movement of the powder inside the enclosure can lead to accidental attachment of powder particles to the walls of the part during the solidification of these walls (cf. FIG. 5).

 This is why it is necessary to design the shape of the solid elements of the powder so that they have good cohesion, while being able to be washed simply during the cleaning of the part. For this, all kinds of "hooked grains" can be conceived, and Figure 6 shows some examples (A to D).

 It is of course possible to mix different kinds of grains in the powder, using the most appropriate grains according to the geometrical characteristics of the different regions of the part.

 To reduce the quantity of polymerized resin in powder form, it is possible to include in suitable places in the powdery medium "bubbles" (not necessarily spherical) of resin surrounded by an enclosure (cf. FIG. 7). The resin included in these bubbles will be reusable for a future production.

 It is necessary to choose judiciously the places where these bubbles are placed, because it is possible that a bubble is too large to be evacuated from the part at the end of the manufacture (cf.

figure 8). This problem can be circumvented either by not putting bubbles in the hardly accessible places of the room, or by putting bubbles of sufficiently small size to not interfere during the cleaning phase.

 Still for the sake of simplification of the final cleaning phase, it may be advantageous to facilitate this task by adopting for the bubbles and the enclosure a production of contiguous shells not attached to each other (cf. FIG. 9). Thus, the extraction of the part from the enclosure and the recovery of the resin in the bubbles will be considerably facilitated.

 To ensure sufficient holding of these shells during the handling of the part preceding its cleaning (leaving the tank and transport to the cleaning area), the shells, and in particular those which make up the enclosure, can be attached to each other by "bridges" of material (see Figure 10), or even hinges (see Figure II). The separation of the shells is then done by breaking or opening these fastening systems.

 The description which follows with reference to the appended drawings will explain in more detail how the invention can be implemented.

 Figure 1 explains 3 intermediate stages in the production of part "P".

 Figure 2 shows how we usually go about solving the problems described in Figure 1.

 Figure 3 shows an example of a room for which it is difficult to set up the technique shown in Figure 2.

 Figure 4 shows the solution adopted for the process which is the subject of this patent.

 Figure 5 illustrates a problem that can occur when implementing the method described in Figure 4.

 Figure 6 shows some examples of grain shapes to solve the problems described in Figure 5.

 Figure 7 shows how the use of bubbles helps preserve fully liquid portions.

 Figure 8 highlights the fact that using grains can solve the problem described in Figure 3.

 Figure 9 shows two examples of decomposition of an enclosure.

 Figure 10 shows an example of possible fasteners to maintain the cohesion of the multiple shells of an enclosure.

 Figure 11 shows an example of possible "hinge" type fasteners to maintain the cohesion of the multiple shells of an enclosure.

 Figure 1 explains 3 intermediate phases in the production of part "P". We see that P has suspended regions "S", that is to say connected neither to the support plate of P, nor to another part of P. During step A, the portion "i" (for " isolated ") the lowest in region S is solidified, but is not connected to solid. After the descent of P into the liquid (ie in step B), the portion "i" of step A can be considered as definitively detached from the part (it now appears as the portion "d" , for "detached"). When we reach step C, the isolated portions "i" of steps A and B are detached, and have become portions "d".

 FIG. 2 shows how one usually proceeds to solve the problems described in FIG. 1. This essentially consists in adding to "P" supports "1", so as not to result in the creation of portions of type "i" or "d", as illustrated in steps A to C corresponding exactly to steps A to C in Figure 1.

 Figure 3 shows an example of a part ("4") for which it is difficult to set up the technique shown in! FIG. 2. It is indeed very difficult to evacuate after manufacture (via the orifice "3") a possible support responsible for allowing the manufacture of the region "2": this would be completely inside of "4", and would therefore be forced to go through "3".

Note: For reasons of readability, the objects listed
in Figures 4, 7 and 8 are hollowed out by a quarter.

 The solution adopted for the process which is the subject of this patent is described in FIG. 4. With the part "P" are associated a set of grains "G" and an enclosure "E", so that their simultaneous manufacture leads to a group of parts avoiding the use of supports, whatever the shape of "P". The enclosure "E" is designed to completely encompass "P", and the grains "G" are arranged between "E" and "P", so that the hanging parts of "P" can be made without adding supports.

 FIG. 5 illustrates a problem that can occur when the method described in FIG. 4 is implemented.

Step A presents the top view of the surface of the liquid during the construction of a part (only the solidified parts "P", "E" and "G" appear), just after a polymerization phase. The device "R" responsible for establishing the next layer of liquid is about to pass over the solidified parts. If the grains "G" are not compacted enough, they will be dispersed by the passage of "R", as shown in step B. During the next polymerization phase, the grains moved to a position too close to " P "may end up being associated with" P ".

 Figure 6 shows some examples of grain shapes "G" to solve the problems described in Figure 5.

 Type A grains form a 3-dimensional block comparable to a brick wall without mortar. Depending on the relative size of the grains with respect to the part, the cohesion of the assembly may be sufficient not to result in a situation like that described in FIG. 5. The "demolition" of this structure during cleaning poses no problem.

 If greater cohesion is necessary, grains of type B to D can be used: they offer good resistance to the passage of a mechanical system for placing the layers if it moves in the direction V. They allow however easy cleaning.

 FIG. 7 shows how the use of bubbles "B" makes it possible to preserve entirely liquid portions "L", by limiting the number of grains "G" to be made compared to the number necessary in the absence of bubbles "B" ( see Figure 4). The amount of solidified (and therefore non-reusable) material can decrease considerably in this way.

 Figure 8 highlights the fact that using grains "G" can solve the problem described in Figure 3. All of the solid parts inside of "P" at the end of manufacturing (the grains , which can be very small) can be discharged through the orifice "3", which would not have been the case if a support had been necessary.

 Figure 9 shows two examples of decomposition of an enclosure, to facilitate its "demolition" when cleaning the room. Example A cuts the enclosure into two shells, and the example cuts it into 4.

 Figures 10 and 11 show examples of possible attachment to maintain the cohesion of the multiple shells forming the enclosures until the final cleaning phase (i.e. during the manufacturing phase, when the part is removed from the when moving it to the cleaning area). The "solid material bridges" PT of FIG. 10 are sufficiently thin (depending on the resin) to be able to be easily broken by hand. FIG. 11 shows an example of a "hinge" CH, making it possible to hold the shells together.

References [1l JC André, A. Le Mehauté, O. De Witte, French Patent
"Device for producing a part model
industrial ", filed 07/16/84. NO 84 11 241 t2] -JC André, M. Cabrera, JY Jezequel, P. Karrer, Patent
English "Process and device for producing models
of industrial parts by the action of light ",
filed on 19/05/88. NO 88 06 708 t3] SCIENCE AND TECHNOLOGY NO 2, February 1988 [4] INDUSTRIAL LASER REVIEW, vol. 2, NO 8, January 1988,
pages 11-37.

[5] 2nd International Conference on Rap id Prototyping, pp
29-38, Dayton, June 23-26, 1991

Claims (10)

Claims  1) Method for manufacturing a set E of three-dimensional solid parts by phototransformation of a liquid organic material which can be polymerized or crosslinkable, by absorption of light by photoinitiators for polymerization or crosslinking, comprising  a) At least one source of light radiation  b) Means of automatically establishing and superimposing  thin layers of the material  c) Optical means allowing the light to be confined  issued by a) in the form of at least one point of impact  on the material  d) Means for automatically moving said (said)  impact point (s) on the material  e) a calculation and storage system making it possible to:  - memorize the geometric shape of the set E  - calculate a set of elementary volumes such  that once phototransformed, these volumes  to them all constitute a set F  of parts such that E is included in F.  necessary for manufacturing.  - control and pilot all automated components  characterized in that in the set F of parts produced for the manufacture of the set E of the desired parts, there is included a set G of solid grains forming, during the manufacturing phase, a more or less fine powder (of the material once phototransformed) mixed with the material still in liquid form, said grains not necessarily all having the same geometric shape.  2) A method according to claim 1 characterized in that in the assembly F (parts actually produced) is included a unit C containing at least one enclosure (hollow hollow part in one piece or composed of several contiguous parts).  3) Method according to claim 2 characterized in that at least one of the elements of C completely encompasses at least one element of E (one of the desired parts).  4) Method according to claim 2 characterized in that the volume encompassed by at least one of the elements of C is entirely in liquid form at the end of the manufacturing.  5) Method according to claims 3 and 4 characterized in that each element of G (solid grains) is located inside an element of C (enclosure).  6) Method according to claim 5 characterized in that at least one element of C includes a volume occupied exclusively by elements of C and / or E, and / or by medium V (composed of elements of G) .  7) Method according to claim 1 characterized in that the elements of the set G are nested between them.  8) Method according to claim 2 characterized in that at least one element of C is composed of several contiguous parts connected together by an easily broken or openable fastening system.  9) Method according to claim 8 characterized in that the fastening system is a hinge  10) Method according to claim 8 characterized in that the fastening system is a bridge of sufficiently fine material to break by hand without effort.